Hindawi Journal of Analytical Methods in Chemistry Volume 2017, Article ID 5391832, 12 pages https://doi.org/10.1155/2017/5391832 Research Article Development of a LC-MS/MS Method for the Simultaneous Detection of Tricarboxylic Acid Cycle Intermediates in a Range of Biological Matrices Omar Al Kadhi,1,2 Antonietta Melchini,1 Richard Mithen,1 and Shikha Saha1 1 Food and Health Programme, Quadram Institute Bioscience, Norwich NR4 7UA, UK 2Department of Urology, Norfolk and Norwich University Hospitals NHS Foundation Trust, Norwich NR4 7UY, UK Correspondence should be addressed to Shikha Saha; [email protected] Received 27 February 2017; Accepted 5 June 2017; Published 18 September 2017 Academic Editor: Nuria´ Fontanals Copyright © 2017 Omar Al Kadhi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. It is now well-established that perturbations in the tricarboxylic acid (TCA) cycle play an important role in the metabolic transformation occurring in cancer including that of the prostate. A method for simultaneous qualitative and quantitative analysis of TCA cycle intermediates in body fluids, tissues, and cultured cell lines of human origin was developed using a common C18 reversed-phase column by LC-MS/MS technique. This LC-MS/MS method for profiling TCA cycle intermediates offers significant advantages including simple and fast preparation of a wide range of human biological samples. The analytical method was validated according to the guideline of the Royal Society of Chemistry Analytical Methods Committee. The limits of detection were below 60 nM for most of the TCA intermediates with the exception of lactic and fumaric acids. The calibration curves of all TCA analytes 2 showed linearity with correlation coefficients > 0.9998. Recoveries were >95% for all TCA analytes. This method was established taking into consideration problems and limitations of existing techniques. We envisage that its application to different biological matrices will facilitate deeper understanding of the metabolic changes in the TCA cycle from in vitro, ex vivo, and in vivo studies. 1. Introduction for lipid synthesis [7]. The different metabolic fate of citrate between healthy and cancer cells has been the focus of Thetricarboxylicacid(TCA)cycle,alsoknownasKrebs’ attention of several research groups, and has been studied cycle, represents a crucial metabolic pathway in almost as possible adjunct to diagnosis and a target for cancer alllivingorganisms[1].Itencompassesacyclicseriesof therapy [8–12]. Many of published reports on the analyses of reactions that oxidises citrate to generate NADH (reduced intermediates of the TCA cycle, including citrate, have used form of nicotinamide adenine dinucleotide, NAD) and a enzymatic or Nuclear Magnetic Resonance (NMR) methods series of metabolites that can be used for amino acid for their detection and quantification [5, 13–15]. Studies that and lipid synthesis, as well as the regeneration of citrate used enzymatic methods often relied on spectrophotometric through the condensation of acetyl CoA with oxaloacetate methods and thus provide indirect measurement of citrate (Figure 1) [2]. NADH feeds into oxidative phosphorylation and related TCA cycle intermediates [16–18]. NMR offers to generate adenosine-triphosphate (ATP) [3]. In certain the advantage of requiring minimal sample preparation but cell types and pathological conditions citrate is exported lacks the sensitivity in comparison to liquid chromatography from mitochondria as opposed to being oxidised [4, 5]. For (LC) [19]. Analysis of small molecules using targeted liquid example, healthy prostate epithelial cells have a modified chromatography tandem mass spectrometry (LC-MS/MS) is TCAcyclethatfavourstheexportofcitrateoutofthe thought to provide higher sensitivity especially from matrices mitochondrion to provide an energy source for spermatozoa where compounds or molecules are at low concentrations [6]. Likewise, many cancer cells favour the export of citrate [20, 21]. Our aim was to develop a LC-MS/MS method 2 Journal of Analytical Methods in Chemistry O OH O OO O OH HO OH HO OH HO O OH O O Citric acid -Ketoglutaric acid Succinic acid O O OO HO HO HO OH OH OH O OH O O Fumaric acid L-Malic acid Oxaloacetic acid Figure 1: Chemical structure of TCA cycle intermediates. that would allow the simultaneous detection of TCA cycle 2.2. Human Body Fluids. For purposes of method develop- intermediates in different biological matrices of human origin mentandwithlocalethicalapproval,urine(=5)and with a relatively easy sample preparation and high sensitivity. plasma (=10) samples were obtained from healthy subjects. Previous studies have described the application of liquid Plasma samples (10 l) were mixed with 5% trichloroacetic chromatographic methods coupled with mass spectrometry acid (80 l) and 0.1 mg/ml internal standard (deuterated D4- for the determination of specific intermediates of the Krebs citric acid, 10 l). The mixture was vortexed for 30 seconds cycle (e.g., succinic acid, citric acid) in body fluids [22, 23]. and kept on ice for 5 minutes (vortex twice/2 minutes). ∘ The simultaneous determination of TCA intermediates has Samples were centrifuged at 17,000 ×gfor10minutes(4C) been described in natural waters or bacterial cultures [24– and supernatants were transferred to HPLC vials for analysis 26], but there are only few reports in samples of human origin by LC-MS/MS. After filtration by using a minisart Sterile- including tumour specimens [27–29]. This study reports the ED 0.20 mfilter,urinesamples(10l) were added to development and validation of an extraction method from 0.2% formic acid (80 l) and 0.1 mg/ml internal standard human plasma, urine, prostate tissue, and cultured cells that (deuterated D4-citric acid, 10 l). The mixture was vortexed allows the qualitative and quantitative analysis of TCA cycle for 30 seconds and kept on ice for 5 minutes (vortex twice/2 intermediates by using LC-MS/MS. It was envisaged that minutes). Samples were then centrifuged at 13,000 ×gfor5 ∘ the simultaneous detection and quantification of these key minutes (4 C). Supernatants were transferred to HPLC vials metabolites by LC-MS/MS could be a useful research tool and andanalysedbytheLC-MS/MSonthesameday. may provide a more holistic picture of the changes that occur in the TCA cycle in different cancer types including prostate 2.3. Human Prostate Tissue. Frozen samples of histologically cancer. proven benign (=5) and cancer (=5) prostate tissue were obtained from the Norwich Biorepository (Norfolk and 2. Experimental Norwich University Hospital Human Tissue Bank). Benign tissue samples were obtained from patients undergoing 2.1. Chemicals and Reagents. Tricarboxylic acid standards radical prostatectomy for organ confined prostate cancer. [glutamic acid (≥99%),citricacid(≥99%), isocitric acid The protocol was approved by the Faculty of Medicine and (≥93%), -ketoglutaric acid (≥99%), malic acid (≥99%), Health Science Research Ethics Committee in January 2013 − ∘ oxaloacetic acid (≥97%), succinic acid (≥99%), and fumaric (Reference: 2012/2013-37). Tissue samples were kept at 80 C acid (≥99%)] were purchased from Sigma5 (Sigma-Aldrich until pulverized with liquid nitrogen using a tissue grinder Company Ltd., Dorset, UK). Lactic acid (≥85%) was also (BioPulverizer, Stratech Scientific Limited, Newmarket, UK). obtained from Sigma (Sigma-Aldrich Company Ltd., Dorset, 500 l of 3 M perchloric acid was added to each 20 mg UK). Deuterated D4-citric acid (2,2,4,4-D4, 98%) was pur- of tissue powder and homogenised using an automated chased from Cambridge Isotope Laboratories, Inc. (CK tissue homogeniser (IKA Ultra-Turrax T8 Disperser, Fisher Isotopes Ltd., Leicestershire, UK). Synthetic urine con- Scientific Ltd, Loughborough, UK) for 1 minute on medium trol sample and fatty acid-free human serum albumin speed. The homogenate was left on ice for 10 minutes ∘ (HSA) were purchased from Sigma (Sigma-Aldrich Company and then centrifuged at 12,000 ×gfor10minutesat2–4C. Ltd., Dorset, UK). Trichloroacetic acid and perchloric acid Supernatants were transferred to HPLC vials and analysed by were purchased from Sigma (Sigma-Aldrich Company Ltd., the LC-MS/MS on the same day. Dorset, UK). Water was obtained from a Milli-Q5 Integral Water Purification System (Millipore Limited, Hertfordshire, 2.4. Human Cell Lines. Human cancerous prostate ade- UK). nocarcinoma (PC3) cells were purchased from European Journal of Analytical Methods in Chemistry 3 ∘ Collection of Authenticated Cell Cultures (ECACC) (number injection volume and the autosampler was maintained at 4 C. 90112714). Cells were routinely cultured as monolayers in The Agilent 6490 Triple Quad LC-MS/MS system comprised Ham’s F-12 medium supplemented with 10% foetal bovine a degasser, binary pump, cooled autosampler, column oven, ∘ serum (FBS) in a humidified atmosphere containing 5%2 CO and 6490 mass spectrometer. The gas temperature was 200 C ∘ ∘ at 37 C. The culture medium was changed every two days. and flow was 16 l/minute; sheath gas temperature was 300 C Cells were grown to 80% confluency on 10 cm dishes before with flow of 11 l/minute and nebuliser pressure of 50 psi. ∘ ∘ performing the extraction of the TCA cycle intermediates. Capillary voltage was 3500 C and 3000 Cforpositiveand Briefly, cells were washed twice with 10 ml 0.9% sodium negative